As to methods for preparing cyanoacetic acid esters, there have been generally well known various methods, such as a method of reacting a chloroacetic acid ester with NaCN or KCN; a method of reacting a cyanoacetyl halide with an alcohol in the presence of a basic catalyst; a method of alkoxycarbonylation by reacting a chloroacetonitrile with CO and an alcohol; a method of subjecting a cyanoacetic acid with an alcohol to dehydrating reaction in the presence of an acid catalyst; and a method of transesterification by subjecting a cyanoacetic acid ester with an alcohol.
For example, as to methods for preparing t-butyl cyanoacetate, there have been known: 1 a method of reacting t-butyl chloroacetate with NaCN or KCN [DE 1951032; Helv. Chim. Acta., 42, 1214, 1222 (1959); J. Am. Chem. Soc., 64, 2274 (1942)], 2 a method of reacting a cyanoacetyl halide with t-butanol and N,N-dimethylaniline [J. Chem. Soc., (1955), 423,426; Org. Synth., Coll. Vol. 5, 171]; and 3 an alkoxycarbonylation method by reacting chloroacetonitrile with CO and t-butanol [DE-2403483].
However, the method of 1 requires t-butyl chloroacetate as the raw material, which is not easily available and should be prepared separately through a complicated route. Furthermore, according to this method, there is troublesome problem that a large amount of waste matter such as NaCl, a by-product of the reaction, is produced. Also, the method of 2 uses necessarily PCl.sub.5, which is highly corrosive compound, for obtaining cyanoacetyl halide as the raw material, and for this reason the construction materials of the equipment for producing the same are greatly restricted. Additionally, an equimolar or excess quantity of N,N-dimethylaniline is required to an equimolar quantity of cyanoacetyl halide. In accordance with proceeding of the reaction, the hydrochloride of N,N-dimethylaniline is by-produced and also a large quantity of other waste matter in produced. Furthermore, the method of 3 is restricted greatly with respect to the equipment for the reason that CO should be reacted under a high pressure.
The method of dehydrating reaction by subjecting cyanoacetic acid with an alcohol in the presence of an acid catalyst is disclosed in some literatures, for example, Ann. Chim., (Paris), 9 (9), 69 (1918); and Tetrahedron, 305, (1967). The reactivity of this method is excellent when an alcohol having a small number of carbon atoms, especially a primary alcohol is used. However, this method shows drawback that the reactivity is lowered when a higher alcohol or tertiary alcohol is used. Furthermore, this method is not adapted for preparing a tertiary ester of cyanoacetic acid which is unstable to an acid.
Additionally, as to the methods of transesterification of a cyanoacetic ester with an alcohol, use of a titanium alkoxide as a catalyst is known [Org. Synth., 65, 230, (1987); Helv. Chim. Acta., 65, 1197, (1982); Helv. Chim. Acta., 65, 495, (1982); and Synthesis, (1982), 138]. However, these literatures indeed disclose reactions by using alcohols such as primary or secondary alcohols, such as methanol, ethanol and isopropanol; but these literatures do not disclose a reaction by using a tertiary alcohol such as t-butanol or the like, which is known to be unsuitable for the transesterification. There have not been found any literature which discloses a transesterification between a cyanoacetic acid ester and t-butanol.
The present invention have been completed to solve the above-mentioned various problems in the prior art, and an object thereof is to prepare cyanoacetic acid higher esters in higher yield by using cyanoacetic acid esters and alcohols as the raw materials which are less expensive and easily available.